Color television apparatus



April 12, 1960 A. I IEBscHER coLoR TELEVISION APPARATUS Original Filed Sept. 23, 1952 5 VJ l y n 1ML] MPE E /J 1M MU lww/ im Mf/.H d W mi 0 i #1% WM m M mw w n m. l lMHHWMW. V50 of luvllllln.. y M w /N M6 @l M /Vv/V//hf 4 T/Nw w @j M f ||||hF||.||/ iwi y m t" I@F i 0% a0 M n i /wu y /l VW .M z .Mw M m n n a H M d 0 11 1: 7 7 :l M a M i n. :I: YK D. 5 .llfl IIIHHIIL A 5M Lr LM f F w MM 6 H/ f m J Nr j 0T1 n E al 1111 /z ff 7 WHW/WJ. ,mum v 5 5 lllllL x W United States Patent() 2,932,756 coLoR TELEVISION APPARATUS Arthur Liebscher, Jenkintown, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application September 23, 1952, Serial No. 310,944,

w ch is a continuation of abandoned application Serial Noz 4,660, January 27, 1948. Divided and this application February 27, 1956, Serial No. 568,110

14 Claims. (Cl. 313-92) This invention relates to color television and particularly to the pickup, transmission Aand reproduction of images in substantially their natural color.

This application is a division of application Serial No. 310,944, filed September 23, 1952 which, in turn, is a continuation of application (now abandoned) Serial No. 4,660, tiled January 27, 1948, and entitled Color Television System.

Images in substantially their natural color may be transmitted over electrical circuits by analyzing the light from the object into not only its -image elements, but by also analyzing the light ofthe object into selected primary or component colors and deriving therefrom signal trains of impulses representative of each of the selected component colors. The image in substantially its natural color may then be reproduced at a remote location by appropriate reconstruction from the component Color signal trains. Y

The transmission and reproduction of color images may be accomplished by either of two fundamental systems of multiple image transmission which have become widely known as the simultaneous and the sequential systems of color image transmission.

The simultaneous system transmits all component color signal trains simultaneously through three separate signal channels.

' The sequential system transmits at any one` timeonly one component color signal train, and transmits in predetermined sequence a portion of each of the selected component color signal trains.

The device employed for converting light from an object into a signal train is commonly known as a television camera. In the transmission of images by the sequential method, the camera may have a single image pickup tube, such as, for example, the so-called image orthicon, which is exposed in succession to images giving color separation corresponding to the various selected component colors. During the period that the camera tube is exposed to each color component image, the mosaic is concurrently scanned to enable the transmission of signals representing the corresponding color ,separation image.

Image pickup tubes may take variousforms. An image orthicon camera is shown and described in an article 4entitled Image Orthicon Camera by R. D. Kell and G. C. Sziklai in the RCA Review for March 1946.

In the conventional sequential multicolor television receiver, `a kinescope or other image producing tube is employed to recreate a black and white image likeness which is viewed or projected through a color tlter of the selected component color corresponding to the desired component color instantaneously being represented. The process is then repeated for the next selected color component, and so on. A typical sequential color television system is shown and described in an article entitled 1An Experimental Color Television System, `begnnu'ng Lon page i141 of the RCA Review for June 1946.

Although color images have been successfully repro- 2,932,756 Patented Apr. 12, '19605 duced by the aforementioned sequential method, there are certain fundamental diiculties involved which tend to reduce the entertainment value of the sequential system. Typical diiculties involved include color action fringes, resulting from movement between individual component color scannings, and inadequacy of illumination, which results from the required division of available light for the reproduction in a sequential manner of the individual selected color component images.

The lundamental diculties, particularly the color action fringes, referred to above for the sequential method are eliminated if the rate of change between the selected component colors is' made rapid enough to overcome any indication of movement between the different selected component color representations.

lf, for example, an elemental sequential rate is employed, that is, if each image element yis divided into three selected component colors, and for each elemental area of the image there are transmitted `sequentially three different color representations, each of whose amplitude or energy depends upon the selected color components of the image element, no difliculty will be experienced with color action fringes.

It becomes apparent, however, that such an arrangement would require not only accurate synchronism in the scanning raster, but it would require also proper color phasing by such means as maintaining an accurate syn chronism or speed control in each traverse of the scanning element in order that the corresponding color representation at both the transmitter and receiver would be scanned in perfect synchronism.

According to this invention, an improved method and arrangement is provided whereby color television signals are transmitted in an elemental sequential arrangement andthere is employed a sweep speed synchronizing pulse having a repetition rate at elemental frequencies. In one form of the invention, the sweep speed synchronizing pulse is developed in the transmitter by employment of a strip type filter involving not only the red, blue and green components, but also an ultraviolet filter for prof ducing a uniform signal iiripulse upon scanning. In the receiver, the sweep speed synchronizing pulse is compared with a pulse developed by the scanning operation in the receiving tube. The two sweep speed pulses are compared to control the sweep speed in the image reproducing tube, whereby to eect the desired color phasing.

A primary object of this invention is therefore to provide an improved color television system.

Another object of this invention yis to eliminate color action fringes in sequential color television systems.

Still another object of this invention is to eliminate registration problems in color television systems.

Still another object of this invention is to maintain accurate sweep speed synchronism at the receiving station with the sweep speed of deflection at the transmitting stations.

Other and incidental objects of the invention will be apparent rto those skilled in the art from a reading of the following specification and an inspectionr of the accompanying drawing in which:

Figure 1 shows in block diagram one form of this invention as it may be employed at the transmitting stations;

Figure 2 illustrates a greatly enlarged section of an electron beam scanning target; and

Figure 3 `shows by block and cirouit diagram one form of this invention suitable for employment at the receivin stations.

Turning now in more detail to Figure l, there is shown a transmitting tube 1, which, in general, may take any of the well-known forms. As shown, it takes the form 3 ot the well-known image orthicon type tube which is well shown and described in an article entitled The Image Orthicon, A Sensitive Television Image Pickup Tube, published in the Proceedings of the Institute of Radio Engineers for July 1946.

; Although details regarding circuit arrangements for maintaining deection and focus of the scanning beam are'V not shown or described in detail, it is believed thatvarious arrangements for accomplishing deiiection and focus` are well-known in the art and need no detailed description here. The transmitting tube 1 does, however, have an .irnportant difference from `that shown and described in the published art. This difference, in accordance with this invention, may be found in the structure of the target 3, which consists, in one form, of a plurality of similar groups of strip-like sections, each strip-like section of a group being limited in its representation to one diiferent selected color component of a corresponding image sectional area or a reference signal impulse forming area.

brief reference to Figure 2 will more clearly illustrate the form of the electron beam target 3 of Figure 1.

In Figure 2, the photo-emissive material 5 is located on the back of the similar groups of strip-like sections involving, as illustrated, filter elements of red, blue and green, together with a iilter element of ultraviolet.

Although the target section shown in Figure 2 includes filter elements, the target structure may include, for transmitting purposes, a color sensitive photo mosaic surface. Another alternate arrangement may be employed Vwhen target 3 of Figure 1 is used in a transmitter tube without an image section. It will be seen that in the form of the invention shown in Figure 1, the target 3, involving the strip-like sections is not the target upon lwhich thek electron scanning beam ofthe tube 1 impinges. Target 7 of tube 1 is impacted by the electron beam of tube 1. Inl accordance with a well-known theory of the image tube, the target 3 .produces an electron image which is electrically focussed on target 7.

Turning again to Figure 2, it follows that lif the light approaches from the front, the photosensitive area 5 will have an electrical representation developed thereon, depending upon the color of the incident light and the color of the associated iilter section. If, for example, a 4,red-light is projected upon the target 3 from the object 9 of Figure 1, only that portion of the photosensitive element 5 behind the red filter sections will be activated. Therefore, the signal developed by the scanning operation of tube I will provide signal impulses only at the time 'the electron scanning beam scans the area of target 7 corresponding to the area behind each of the red filter sections of target 3 of tube 1. This `is true for each of the 'selected component colors.

If, however, a lamp 11 is provided with an ultraviolet iilt'er 13 in order to provide a constant illuminationof ultraviolet light on electrode 3, a series of substantially :uniform pulses will be developed as the scanning beam traverses target 7. A pulse will be formed each time the scanning beam traverses a section of target 7 which corresponds to the section of electrode 3 which is immediately behind the ultraviolet filter sections.

It will therefore lbe seen that if no light is projected on electrode 3 from object 9, and if lamp 11 illuminates electrode 3 with an ultraviolet light, a series of impulses will' be developed in transmitter tube 1 whose rate of recurrence is equal to the rate of deflection of the scanning beam across the ultraviolet filter sections.

If, yfor example, the lter sections illustrated in Figure -2 are made of a size such that each group of filter sections involving a red, blue, green and ultraviolet section is made to correspond with an image element size, the

ksignal impulses generated by the scanning of the ultraviolet `filter sections will correspond to an elemental frequency.

It` this beam traverse speed control signal developed 4 by the scanning operation of transmitting tube 1 is'transmitted, together with video signals developed as a result of the light projected on electrode`3 by colored object 9, the combination may be employed at the receiver for not only the reproduction of images, but also the receiving system scanning traverse speed control.

In the form of the invention shown in Figure l, the signal developed by the. transmitter tube lis amplified in video amplier 15 and caused tornodulate the television transmitter 17 by modulator 19.

Modulator 19 also receives a deiiection synchronizing signal from sync generator 2d. The deiiection synchronizing signal of synchronizing generator 2l `is also employed in the well-known manner for the control of horizontal deflection and'vertical deflection of the transmitter tube 1 through horizontaldeiiection control 23 and vertical deflection control 25.

Turning now to Figure 3, there is illustrated a television Y receiver 27, which 'may take any of the well-known forms capable of the. reception of a relatively wide signal pass band.

Video. amplifier 2,9. provides the control electrode 3l of image reproducing tube 33 with potential variations to control the intensity of the developed scanning beam in accordance, with. the. video signal.

The image reproducing tube 33 may take, in general, any of the well-known forms, such as, for example, the popular kinescope, which is well described in the .published art.

There is, however, an important difference in the kinescope 33 modified to operate in accordance with this invention. The diierenceresides in the screen 35 which, in ther form of the invention shown, takes the form of adjacently positioned and similar groups of strip-like sections, wherein each strip-like section of the group is limited in its effective reproduction to one different selected color component of the corresponding image sectional area. The enlarged view of the multiple target Y may take the form of that shown in Figure 2, wherein the red, blue, green and ultraviolet ijlter sections are applied to the light producing element, which might take the fwn 0f a White. phosphor 5- The beam generation and deflection involved in kinescope 33 follows the well-known forms of employing a deflection sync separator 37 and producing from the separatedsynchronizing impulse a horizontal sweep frequency in horizontal sweep oscillator 39, and a vertical sweep lsignal in vertical sweep oscillator 41.

The appropriateL sweep energy is applied to horizontal and Vertical deflection coils 43 and 45, also in the wellknown manner.

As has been outlined above, it is necessary,.for accurate color. representation, to employ careful synchronism in not only, deflection, but in the rate or speed of deflection.

The sweep speedvis controlled by obtaining from video amplilier- 29 the sweep speed synchronizing impulses` developed at the transmitting station, as described above under Figure 1. This is accomplished by a clipping action in tube 47, which is appropriately biased to clip off only a .portion of the signal train developed in video amplifier 29. In the form of the invention shown, this sweep vspeed synchronizing pulse is developed in a white direction.

`The sweep speed synchronizing pulse is then transmittedto a sweep speed control, illustrated by dotted block 49, which operates to compare the sweep speed synchronizing pulse obtained from the transmitting systernr with the impulses developed at photocell 51, which is locatedr behind an ultraviolet lter 53, with respect to the screen 35 of image reproducing tube 33.

As vthe electron beam of kinescope 33 scans the target 35, an impulse will be formed in tube 51v each time the scanning beam traverses the ultraviolet lter section of target 35. Due to the limitation of ultraviolet filter 53, no limpulses will be Yfornued in photoelectric cell 51 while the v"scanning beam is scanning the red, A,blue or'green iilter sections of target 35.

I If the signal pulses obtained in photocell '1 arecompared with the sweep speed synchronizing pulses obtained from the transmitter, it will be seen that an accurate sweep speed synchronization may be obtained between the scanning beam of the transmitter tube 1 and the scanning beam of the receiver tube 33. If, then, the order of the filter sections of the target 3 of Figure 1 and the target 35 of Figure 3 is arranged in the same order, it will be seen that the scanning beams of both the transmitter tube 1 of Figure l and the receiving image produced on target 35 will correspond precisely, and the resultant image produced on target 35 will correspond to the image projected on the target 3 of Figure 1.

Although various arrangements are available for comparing the synchronizing sweep speed impulse with the impulses derived from photocell 51, the circuit arrangement shown in Figure k3 is given by way of example.

The sweep speed control circuit 49 involves a phasesplitter amplifier 55, which develops,together with diodes 57 and 59, a'voltagewhich is dependentA upon the synchronism `of the sweep speed synchronizing signal -derived from the transmitter and the impulsesobtained from photocell 51. l The operation of the circuit arrangement employed for sweep speed c ontrol is well-known in the art andis illustrated in detail in the U.S. Patent No. 2,458,156, ilssued to G. L. Fredendall.

It will be seen, after'a brief examination of the circuit arrangement shown in block 49 of Figure 3, that the potential applied to the control electrode 61 of tube 63 is dependent upon whether or not the impulses derived from photocell 51 lead or lag the impulses of the sweep speed synchronizing impulses obtained from the transmitting system.

It therefore follows that the output signal obtained from tube 63 is dependent upon the sweep speed of the electron beam developed in receiving tube 33.

The output energy from tube 63 may therefore be applied to horizontal deflection coils 43 or it may be applied to an auxiliary horizontal deection coil not shown. It will be seen, therefore, that the output energy of tube 63 will control the sweep or traverse speed of the scanning beam of image reproducing tube 33 to synchronize accurately with the scanning speed of the electron beam developed in transmitter tube 1 of Figure 1.

This accurate control of sweep speed of the scanning 'beam of tube 33 will result in accurate registration of corresponding color filter sections of both reproducing tube 33 and transmitter tube 1.

Having thus described the invention, what is claimed 1s:

l. An electron scanning beam target comprising in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uniform width, the strip-like sections of each group being representative respectively of different image component colored lights and of a reference signal impulse, each strip-like section of a group limited in its representation to one different selected component color and a reference signal impulse forming area.

2. An electron scanning beam target comprising in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uniform width, the striplike sections of each group being representative respectively of different image component colored lights and of light of an invisible color, each striplike section of a group limited in its representation to one different selected component color, including an invisible component color.

3. An electron scanning beam target comprising in combination a plurality of repeating, adjacently posi- Vtioned and similar groups of strip-like sections of uniform -width, the strip-like sections of each group being respectively responsive to dier'ent image component colored lights and light of an invisible component color, each strip-like section of a group, limited in 'its responseto one dilferent selected component color, including ,an invisible component color.

4. An electron scanning beam target comprising in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uniform width, the strip-like sections of each group being reproductive respectively of diierent image component colored,

lights and of an invisible component color, each strip-jy like section of a group limited in its reproduction to one different selected component color, including an invisible component color. i

'5. An electron scanning'beam target comprising in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uni form width, the strip-like sections of each group being representative respectively of substantiallyred, blue and green image component colored lights and of a reference signal, and wherein each group includes at least one each section representing the substantially red component, the substantially blue component, the substantially green component, and a reference signal forming area.

6. An electron scanning beam target comprising, in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uniform width, the strip-like sections of each group being representative respectively of substantially red, lblue and green image component colored lights and of light of an invisible component color, and wherein each group includes at least one each section representing the substantially red component, the substantially blue component, the substantially green component, and an invisible color component.

7. An electron scanning beam target comprising in combination a plurality of repeating, adjacently positioned and similar groups of strip-like sections of uniform width, the strip-like sections of each group being representative respectively of the substantially red, blue and green image component colored lights and of light of an ultra-violet component, and wherein each group includes at least one each section representing the substantially red component, the substantially blue component, the substantially green component, and an ultra-violet component.

8. Color television image reproducing apparatus having a luminescent screen for producing a color image when impinged by an electron beam, said screen including a plurality of groups of strip-like regions respectively adapted for light emission in the colors in which said image is to be reproduced, and a plurality of strip-like indexing elements placed near said strip-like light-emitting regions and adapted to emit radiant energy distinctive from said light emission when impinged by an electron beam.

9. Color television image reproducing apparatus having a luminescent screen for producing a color image when impinged by an electron beam, said screen including a plurality of groups of strip-like regions respectively adapted for light emission in the colors in which said image is to be reproduced, and a plurality of strip-like indexing elements placed near said groups of strip-like light-emitting regions and adapted to emit light having a distinctive color from said light emitted from said striplike regions when impinged by an electron beam.

10. Color television image reproducing apparatus having a luminescent screen for producing a color image when impinged by an electron beam, said screen including a plurality of groups of strip-like regions respectively adapted for normally visible light emission in the colors in which said image is to be reproduced, and a plurality of strip-like indexing elements placed near those ones of said strip-like light-emitting regions which emit light of a given color, said strip-like indexing elements being 7 adapted to emit normally invisible light when impinged by :an electron beam.r

141.'A .Color television image reproducing .apparatus hav ing a luminescent -sc-reen -.for producing .a color image when impinged by an electron beam, lsaid screen includ-f in'g apluralityrof groups Vofstrip-like regions, the strip-like regions of each lof said `groups -being adapted respectively for emission -of red, green and blue colored lights, and a plurality of strip-like indexing .elements jplaced near those ones of said strip-like light-emitting regions which emit light :of a given one of -said colored lights, said strip-like indexing elements being adapted to emit ultra-violet light when impinged fby an electron beam.'

12. In color television apparatus, a cathode. ray tube having a target `consisting of ,-groupsof parallel lines of material :in sequence, =each Vline in .a group being responsive to color information dilerent from those of the other lines ofeach group, a separating line of material `between successive vgroupsiof li-nes,lsad separating lines `being ,-responsive to radiation 'energy outside of the visible spectrum, means causing the cathode ray beam of said tube to scan said target and :means generating avcolor phasing signal 4each time said `beam crosses one of said separating lines.

v13. In color television apparatus, a cathode ray tube having va target'consisting Aof groups of parallel `lines 'of screen material inisequence,`each line in a group uorecing in acolor 'diierent from those ofother lines of said group, separating lines .of .screen rmaterial between said groups, said separating lines iluorescfing outside .of .the range visible light, .means causing the cathode ray beam of said `tube to scan .said target, and .means generating a .color Iphasing-signal each time. said beam crosses .one of .said separating lines.

14. .Color television image Vreproducing apparatus hav,- ing a luminescent screen for producing a color image when impinged by an electron beam deflected thereover in a .plurality ,of vertically spaced .horizontal lines for-rning a substantially .rectangular area, said screen including a .plurality `of repeating and similar groups of parallel and `adjacently positioned strips of substantially the same width and extending transversely to .the horizontal lines scanned by said beam, each of .said groups including color representative phosphor strips eective respectively to Yproducc light of the component colors of an image when'im? pinged by an electron beam and a .strip effective `to produce acontrol signal when impinged by an electron beam.

References Citedin'the file of this patent UNITED STATES PATENTS 2,490,812 

